The present invention is directed to integrated circuits. More particularly, the invention provides a method and apparatus for testing an oxide layer with fuse. Merely by way of example, the invention has been applied to testing a gate oxide layer. But it would be recognized that the invention has a much broader range of applicability.
Integrated circuits or “ICs” have evolved from a handful of interconnected devices fabricated on a single chip of silicon to millions of devices. Current ICs provide performance and complexity far beyond what was originally imagined. In order to achieve improvements in complexity and circuit density (i.e., the number of devices capable of being packed onto a given chip area), the size of the smallest device feature, also known as the device “geometry”, has become smaller with each generation of ICs. Semiconductor devices are now being fabricated with features less than a quarter of a micron across.
Increasing circuit density has not only improved the complexity and performance of ICs but has also provided lower cost parts to the consumer. An IC fabrication facility can cost hundreds of millions, or even billions, of dollars. Each fabrication facility will have a certain throughput of wafers, and each wafer will have a certain number of ICs on it. Therefore, by making the individual devices of an IC smaller, more devices may be fabricated on each wafer, thus increasing the output of the fabrication facility. Making devices smaller is very challenging, as a given process, device layout, and/or system design often work down to only a certain feature size.
An example of such a limit is testing of a gate oxide layer. FIG. 1 is a simplified diagram showing conventional method and apparatus for testing gate oxide layer. The tested gate oxide layer is sandwiched between two conductive plates 110 and 112. The plate 110 is biased to a ground voltage level by a metal wire 120. The plate 112 is coupled to a source-measure unit (SMU) 130 via a metal wire 122. The source-measure unit 130 can provide a predetermined voltage and measure the resulting current by a probe card 132. During test, a predetermined voltage is provided to the conductive wire 122 by the source-measure unit 130. The resulting current that flows through the conductive wire 122 is measured by the source-measure unit 130. Based on the measured current, whether the gate oxide layer has broken down is determined. If the measured current becomes much higher, the gate oxide layer is determined to have broken down. If the gate oxide layer is determined to have not broken down, another voltage is provided to the conductive wire 122 for further testing. But this conventional method and apparatus for breakdown detection has limited reliability and sensitivity.
From the above, it is seen that an improved technique for testing oxide layer is desired.